Liquid crystal displays (LCDs) are commonly used as display devices because of their capability of displaying images with good quality while using little power. However, liquid crystals in an LCD do not emit any light themselves. The liquid crystals have to be lit up by a light source so as to clearly and sharply display text and images. Usually, a backlight is employed as such a light source. Light emitting diode (LED) array modules have recently emerged as a new backlight source and become increasingly popular.
An LCD backlight typically includes a plurality of red, green and blue (RGB) LEDs, regularly arranged to form a number of LED areas, and driven electrically to produce various colors of light including white light. Generally, the characteristics of individual RGB LEDs varies with the temperature, driving current, and aging. The characteristics also varies from batch to batch for the same LED fabrication process and from manufacturer to manufacturer. Consequently, the light produced by an RGB LED based backlight module may have non-uniformity of brightness and colorfulness over different LED areas of the backlight module. In addition, the temperature differences between different LED areas are also affected by image data to be displayed on an LCD, and thus are hardly predicted, which may make the non-uniformity of brightness and colorfulness of the light even worse. To ensure an LED backlight to produce light with uniform brightness and desired colorfulness, a suitable feedback control system is usually utilized to monitor the chromaticity and/or brightness (luminescence) of the light emitted from each LED area.
One known feedback system includes a plurality of photo-sensors. Each photo-sensor is configured to individually monitor the chromaticity of the light emitted from a corresponding LED area. The monitored chromaticity of the emitted light is then fed back to a controller that adjusts the driving current of the LED area accordingly, thereby controlling the color of the light emitted from each LED area at a desired chromaticity. Other feedback systems include one or more temperature detectors for monitoring the temperature of each LED area. Then the driving current of each LED area is adjusted according to the measured temperatures. However, such feedback systems require multi-color sensor or temperature sensor to guarantee the uniformity. Thus these systems result in sophisticated control circuitry and are not cost-effective.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.